Initial cell selection is a procedure for a wireless device to determine the presence of a wireless network and find a suitable cell via which to access the network. In the initial cell selection, the wireless device scans a list of possible carrier frequencies of configured operating bands, searches for the cell with the strongest signal strength, finds a cell identification number for the cell with the strongest signal strength, and detects the channel bandwidth and other broadcast information, such as a public land mobile network (PLMN) identification number for that cell. Having found a suitable cell via which to access the network, the wireless device also needs to regularly perform a cell reselection procedure to search for a potentially better cell, which may use a different frequency, via which to access the network. The time required for initial cell selection impacts the end user experience. The time for cell reselection in particular is an important contributing factor to the power consumption of a wireless device.
To speed up the carrier frequency scan, a received signal strength indicator (RSSI) based carrier frequency scan may be employed and the carrier frequencies with strong RSSIs are identified for further cell identification. However, an RSSI scan with a fixed measurement interval may not be effective in determining the signal strength if the measurement interval does not capture the downlink signal with sufficient power. This may happen when a wireless network has no downlink transmission during a portion of the transmission resource designated for uplink transmission in Time-Division Duplex mode, during a portion of the transmission resource designated for Multimedia Broadcast-Multicast Service Single Frequency Network (MBSFN) transmission, but with no MBSFN traffic at that time, or when a weak downlink signal is detected due to propagation loss or deep fading. Conventional approaches for addressing the problem, such as increasing the fixed measurement interval or performing multiple RSSI scan passes, may increase linearly the RSSI scan time and the battery power consumption for all wireless devices. However, as the inability to detect sufficient power occurs in certain cases and not all cases, there is no need to increase the fixed measurement interval all the time.